Raisable flexible skirt for fluidcushion sustained vehicles



June 27, 1967 P. F. GUIENNE ETAL RAISABLE FLEXIBLE SKIRT FOR FLUID-CUSHION SUSTAINED VEHICLES Filed Oct. 18, 1965 NEE J w Q ief/ MMVJ Ww /w run emww M w 0 n% d PH F I Imp M 3 P n United States Patent 3 Claims. {01. 130-7 Various kinds of raisable flexible skirts for vehicles borne by at least one pressure fluid cushion have been disclosed. Inter alia French patent of addition No. 80,047 teaches that such a skirt can be embodied by a number of identical and substantially horizontal inflatable annular tubes being disposed above a frusto-conical portion whose bottom free edge bounds an area smaller than the contact area between the tubes. As a rule, a skirt of this kind, which is in plan preferably circular, tends to be elongated by the action of the internal fluid pressure on the resulting difference surface, and inflating the tubes provides an approximately 30% reduction in the total height occupied by the tubes when completely deflated.

This invention also relates to raisable skirts formed by inflatable annular tubes.

It is a main object of the invention to increase the total height variation which variation of the pressure inside the tubes can provide, so that the craft can pass over large obstacles and the vertical and horizontal flotability of a craft having skirts according to the invention can be controlled.

It is another object of the invention to make the fluid cushions bounded by flexible skirts of this kind self-stabilizing, on the basis that a random increase in the pressure of any cushion leads to a reduction of skirt length.

According the invention, the area bounded by the bottom free edge of the skirt when inflated is greater than the area bounded by the inner contact boundaries between adjacent inflatable annular tubes, more particularly the top tube. The bottom portion of the skirt is in shape frusto-conical so that the pressure of the cushion tends to keep the skirt stretched to its maximum length.

In the case of a skirt which is in plan circular, this is equivalent to stating that the diameter of the bottom edge of the frusto-conical skirt is greater than the diameter of the cicrle forming the inner boundary of the area of contact between two adjacent inflatable annular tubes.

In one advantageous form of the invention, the top edge of the frusto-conical portion of the skirt is secured to the lowest inflatable annular tube near the most outward line thereof when such tube is in the inflated state i.e., along the outside mid-circumferential plane of such tube if the same is toroidal.

Because of the self-stabilising nature of such a skirt, the material used for the tube can be resilient and each tube can be formed by two flat annuli interconnected along their respective inside and outside edges, the same merging with the mid-circumferential planes of the torus which a tube of this kind becomes when inflated.

For a better understanding of the invention and to show how the same may be carried into effect, reference may now be made to the accompanying drawings where- 1n:

FIG. 1 is a diagrammatic view in vertical section and showing half of a skirt according to the invention in the inflated state, and

FIG. 2 shows the same skirt but completely deflated.

Referring to the drawings, a platform 1 is borne by a fluid cushion 2, such as an air cushion supplied by a fan 3 or axial-flow compressor. The cushion is bounded laterally by a raisable skirt which forms a main feature 3,327,799 Patented June 27, 1967 of this invention, has the general reference 4 and can be assumed to be circular in plan.

The skirt is formed by a number of substantially horizontal inflatable annular tubes 4a, 4b 4e and a bottom frusto-conical portion 41. Clearly, the radius of the free bottom edge 5 of the skirt is greater by an amount e than the radium R of the circumference forming the internal boundary of the contact surface between consecutive tubes, including the top tube 4a.

The material used for the skirt 4 can be, for instance, a cloth coated to be impervious to the pressure fluid forming the bearing cushion 2; the coating is preferably rubber-based, and the cloth is reinforced so that the finished product has considerable resilience.

Each individual tube can be formed, for instance, by two flat annuli, as 4g and 4h (which together form the tube 412 in FIG. 2) being sewn and/ or stuck togther along their edges. An extra annulus 6 which may be of reduced width serves to secure the top tube 4a to the platform 1. The bottom portion 4l of the skirt is also secured to the outside edge 7 of the annuli forming the bottom tube 4e. The connection between the part 4l and the edge 7 can be effected conventionally, inter alia by sewing or sticking, or perhaps by a slide fastener permitting release of the skirt bottom portion, the part which wears most. Adjacent tubes, as 4;: and 4b, are interconnected near the radius to the centre of a flat annulus, for instance, by a double seam 8a, 8b.

The various tubes which form a skirt intercommunicate via passages 9 which extend through the annular between-tubes contact surfaces bounded by the seams 8a, 8!). Some system for inflation, for instance, a pump 10 which can be driven in some conventional manner, and a four-way valve 11, enables either a positive pressure (FIG. 1) or a negative pressure (FIG. 2) to be applied to the tubes 4a and so on as required, to raise or lower the skirt 4. Pump speed can be varied to adjust the pressure in the tubes to a desired value. Of course, a number of skirts can be associated with independent means for inflating the tubes to give ready control of the horizontal position of the platform.

As the drawings show, the pressure of the cushion 2, by acting on that portion of the bottom tube 42 which is projected on to an annular zone of width 2, opposes the pressure inside the tubes. Consequently, skirt length can be progressively controlled between the end positions shown in FIGS. 1 and 2 by variation of pump speed or, in wider terms, of the pressure of the system for inflating the tubes; the rigidity of the tube outer casing can also have some effect in this connection.

Clearly also, a random increase in cushion pressure such as may result from the platform moving above a locally raised portion of ground, tends to shorten the skirt 4, so that the peripheral leakage below the skirt bottom edge 5 tends to increase and the initial event tends to be opposed. As the engineer in the art will readily gather, a skirt according to the invention and the cushion bounded by such skirt are statically and dynamically stable.

The invention is not of course limited to the embodiment described in detail and covers embodiments obtainable by the use of equivalent technical means. More particularly, the shape of the skirt 4 in plan can be other than circular. The shape of the tubes 4a and so on may, when the same are in the inoperative state, have a shape other than a flat annulus; for instance, such shape can resemble a portion of a cylinder or a torus.

Instead of the pump 10, a compressed gas bottle can be used. In this case, to maintain the skirts in the raised position after the compressor 3 has stopped, the valve 11 is operated to bring the interior of the tubes 4 to atmospheric pressure, whe-reafter the valve 11 is closed, these two steps being performed before the compressor stops. During a first phase the tubes are compressed by the positive pressure in the cushion, to give the shape shown in FIG. 2. The atmospheric pressure outside the tubes then opposes any increase in tube volume. Consequently, when in its normal position the platform 1 can be in a position away from the ground but without elongation of the skirts; of course, it is assumed that the tubes in which skirt weight produces a negative pressure are hermetic.

If required, two superjacent tubes can be interconnected along just one circumference (which replaces the inside seam 8b in the definition of the width e). Advantageously, in this case, such tubes are connected to the pump 10 by flexible ducting.

What we claim is:

1. A fluid-cushion sustained movable body comprising a platform with an underface, a raisable flexible skirt depending from said underface and comprising a plurality of superposed, generally horizontal, inflatable tubes connected to each other along a junction portion having an inner outline, and a generally frusto-conical lower skirt extension connected to the lowermost tube and having a free lower end bounding an area greater than that bounded by said inner outline, and controllable means for selectively inflating and deflating said tubes.

2. A variable-length flexible skirt designed for bounding laterally a fluid cushion in a fluid-cushion sustained vehicle, said skirt comprising a plurality of superposed, generally horizontal, inflatable tubes connected to each other along a junction portion having an inner outline, and a generally frusto-conical lower skirt extension connected to the lowermost tube and having a free lower end bounding an area greater than that bounded by said inner outline.

3. Skirt as claimed in claim 2, wherein each tube comprises two generally planar annular members of resilient material tightly assembled to one another along the inner and outer peripheries of said members respectively.

References Cited UNITED STATES PATENTS 2,508,304 5/1950 Sturtevant 9--1 l 2,914,779 12/1959 Walker 9-11 FOREIGN PATENTS Ad. 80,047 1/1963 France.

A. HARRY LEVY, Primary Examiner. 

1. A FLUID-CUSHION SUSTAINED MOVABLE BODY COMPRISING A PLATFORM WITH AN UNDERFACE, A RAISABLE FLEXIBLE SKIRT DEPENDING FROM SAID UNDERFACE AND COMPRISING A PLURALITY OF SUPERPOSED, GENERALLY HORIZONTAL, INFLATABLE TUBES CONNECTED TO EACH OTHER ALONG A JUNCTION PORTION HAVING AN INNER OUTLINE, AND A GENERALLY FRUSTO-CONCIAL LOWER SKIRT EXTENSION CONNECTED TO THE LOWERMOST TUBE AND HAVING A FREE LOWER END BOUNDING AN AREA GREATER THAN THAT BOUNDED BY SAID INNER OUTLINE, AND CONTROLLABLE MEANS FOR SELECTIVELY INFLATING AND DEFLATING SAID TUBES. 